In The capacity for acclimatiza tion is possessed in very different degrees by different animals, even by different individuals of the same species, and depends much upon general hardihood. Exactly what changes take place during acclimatization is not known; sometimes the very specific gravity of the ani mal is altered, as when fresh-water fishes be come adapted to the denser water of the ocean; similarly, the normal temperature of the individual may gradually become altered, as in the case of fishes native to cool water, which chance to work up-stream into hot springs and live there at a temperature which would kill normal individuals of the same species. The animals which are most wide spread over the earth are those which have the greatest adaptability to new climates and new conditions of environment, and the best examples of this adaptability are fourid among domestic animals (q.v.). About the middle of the 19th century there was much enthusiasm for transplanting animals from one country to another; but the results have so often been harmful rather than beneficial to the recipients of the new forms that the effort to improve on nature in this way has been abandoned. Con spicuous examples are afforded by the sending of the European rabbit to Australia and New Zealand, where it multiplied so excessively in a favorable climate, with abundant food, and through the almost complete lack of enemies, as to become a nuisance and a menace to the pastoral industry. (See RABBIT). The intro
duction of the agua toads, and afterward of the mungoos (q.v.) into Jamaica, to subdue the rats that were devouring the sugar-cane, had evil results. The spread of the European house sparrow in the United States is another pertinent example. Many highly injurious in sects have been accidentally introduced and ac climatized in America from abroad; and the same is true of other countries. On the other hand a few instances like the acclimatization of the silkworm in Europe, of bumblebees in New Zealand, or of ladybirds in California, have been highly beneficial; while much good has come from stocking new streams with de sirable fishes. Of the several societies founded to promote such transferences, that of Paris (Societe d'Acclimatation) is most important, but latterly has been inactive.
In Human See HYGIENE.
Bibliography.-- 'Variations of Animals and Plants Under Darwin; 'Island Life,' Wallace; (Tropical